IMIS - Marine Onderzoeksgroepen

In 2020, a spatial density model estimating loggerhead density, abundance, and distribution across the Mediterranean Sea was generated as a long-term annual average. The model was adjusted for availability bias using dive data from loggerhead turtles tagged with time depth recorders from multiple regions within the Mediterranean Sea. Geographic extrapolation in areas near surveys was undertaken with caution. Mean abundance for the long-term average model was estimated as 1,201,845 (CV 0.22). This estimate represents the first basin-wide estimate of abundance for this species in the Mediterranean not based on demographic models. This work was funded by the U.S. Navy to assist with assessing risk to protected marine species resulting from military readiness activities.

The data are an annual estimated density of loggerhead turtles, expressed as the number of individuals per square kilometer, within the Mediterranean Sea. The study area was gridded into 5x5 kilometer blocks, the resolution at which density modeling was performed. The study area encompasses all major subregions of the Mediterranean Sea, except the Sea of Marmara, which loggerhead turtles do not frequent. The DENSITY attribute contains the estimated density (individuals per square kilometer) and the UNCERTAINTY attribute contains the estimated coefficient of variation (CV) for the density estimate. The density estimates represent the mean throughout year, averaged for the period 2003-2018. For most of the study area, density was estimated using a habitat-based density model that correlated local abundance observed on systematic line transect surveys with environmental conditions observed at that same location and time. For unsurveyed areas and times, density was estimated by extrapolation. Density was not estimated for nearshore locations and inshore waters as they were often not covered by surveys or lacked reliable remoted sensed covariate coverage. See Sparks and DiMatteo (2020) for more information about the modeling process. The metadata documentation has more information regarding individual attributes.

The shoreline and other geographic features were delinated by NAVFAC from a database provided by the National Geospatial-Intelligence Agency (NGA).